perceived brightness for given wavelength?

Banned

I remember seeing a chart somewhere, though I may be mistaking it for something else.

I know beam diameter and divergence affects this a lot too.

Anyway, same power blue laser (445nm) appears less bright to the human eye than red and green wavelengths.
Is there anyway to find out how bright each wavelength appears to the human eye, or how their brightness compares?

New member

I remember seeing a chart somewhere, though I may be mistaking it for something else.

I know beam diameter and divergence affects this a lot too.

Anyway, same power blue laser (445nm) appears less bright to the human eye than red and green wavelengths.
Is there anyway to find out how bright each wavelength appears to the human eye, or how their brightness compares?

Well-known member

Teej, Pi, thanks, it's nice to see a version of that calculator tool that is working. The one I had been using hasn't been up for a while.
I find it pretty handy to have around for general comparisons, although some have said it's not always accurate.

Banned

Thanks guys.
The only problem I see with the online tools it seems to work fine comparing different wavelengths of same power, but comparing different power of the same wavelength doesn't seem right. 10mW compared to 100mW or 100mW compared to 1000mW of anything says 10x more bright.
I remember someone saying brightness doesn't increase linearly or the same amount as the power increases, more like something like twice as bright if 3 times more power, or something.
Although I might not be remembering it right and these values are about how far the visible beam will travel before fading.

New member

Its along the lines of the inverse square law...but, for watts, if you think about it along the lines of lux vs lumens for example, for a given source with all else being equal, twice the lumens will give twice the lux.

Lux is how bright it looks, and lumens would be the total output.

Does that help?

The 4x as bright to look 2x as bright is more along the lines of distance relationships, and is according to the inverse square law.

Example:

I have a flashlight that puts out 1,000 lumens at 100,000 cd (Lux at 1 meter equivalent).

That means at 100 meters, it will put 10 lux on my target.

If I made that 2,000 lumens with the same beam pattern, I would now have twice that, at 20 lux (Double the lumens per square meter).

If I kept the 1,000 lumens and 100,000 cd, but moved the target to 200 meters, I would drop to only 2.5 lux.

So at double the DISTANCE, the same light is going to make the target appear 1/4 as bright.

And, conversely, the light would need to be 4x brighter to make the target look the same brightness, at double the distance.